IRLF 


QL 

949 

F7 


VITREOUS  BODY 


ITS  ORIGIN,  DEVELOPMENT,  AND  STRUCTURE 
AS  OBSERVED  IN  THE  EYE  OF  THE  PIG 


BY 

ALOISIUS  WILLIAM^FROMM,  o.  F.  M, 

sis  submitted  to  the  Faculty  of  Sciences  of  the  Catholic 
University  of  America,  in  partial  fulfillment  of  the 
requirements  for  the  degree  of 
Doctor  of  Philosophy 


WASHINGTON,  D.  C, 


EXCHANGE 


- 


THE 

VITREOUS  BODY 

ITS  ORIGIN,  DEVELOPMENT,  AND  STRUCTURE 
AS  OBSERVED  IN  THE  EYE  OF  THE  PIG 


BY 

ALOISIUS  WILLIAM  FROMM,  o.  F.  M. 

» t 

liesis  submitted  to  the  Faculty  of  Sciences  of  the  Catholic 

University  of  America,  in  partial  fulfillment  of  the 

requirements  for  the  degree  of 

Doctor  of  Philosophy 


V 


WASHINGTON,  D.  C. 

1021 


TABLE  OF  CONTENTS 

Page 

Introduction    1 

Historical  Sketch 2 

Methods    ! 4 

Investigation : 

I.     Primitive  Vitreous  Body 6 

II.     Period  of  Mesodermal  Invasion  of  Vitreous  Body ....  11 

III.     Permanent  Vitreous  Body 18 

Conclusions 25 

Literature    ,  26 

Explanation  of  the  Figures 31 


INTRODUCTION 

The  origin  of  the  vitreous  body  of  the  eye  has  long  been  in  doubt. 
Even  the  numerous  and  thorough  investigations  of  the  first  decade 
of  the  present  century,  although  clearing  up  many  difficulties  and 
correcting  false  notions,  have  failed  to  bring  a  satisfactory  answer 
to  the  question,  i '  Is  the  vitreous  body  of  the  eye  a  derivative  of  the 
outer  or  middle  germ  layer ;  is  it  an  ectodermal  or  mesodermal  for- 
mation?" A  glance  at  some  of  the  latest  and  most  widely  used 
textbooks,  chosen  at  random,  reveals  the  uncertainty  existing  among 
modern  authors  as  to  the  origin  of  this  interesting  structure  of  the 
eye.  Says  Parker  (page  113),  "Mesoderm  also  makes  its  way  into 
the  optic  cup,  through  the  choroid  fissure,  and  becomes  the  vitreous 
humour."  Lillie,  on  the  other  hand,  maintains  (page  275)  the 
"researches  of  the  last  few  years  have  demonstrated  that  the  vitre- 
ous body  is  primarily  of  ectodermal  origin,  its  fibers  arising  as  pro- 
cesses of  cells  of  the  inner  layer  of  the  optic  cup  and  the  matrix 
as  secretion."  Again,  Prentiss  and  Arey  assert  (page  381)  that 
"the  vitreous  body  may  be  regarded  as  a  derivative  both  of  the 
ectoderm  and  the  mesoderm. ' ' 

The  reasons  for  this  diversity  of  opinion  among  biologists  may  be 
reduced  to  the  following :  1.  The  very  delicate  nature  of  the  vitre- 
ous body,  which  differs  so  widely  from  all  other  tissues,  renders  its 
study  extremely  difficult.  It  requires  special  methods  of  technique 
not  ordinarily  employed  in  histological  investigations.  The  diffi- 
culties of  obtaining  perfect  sections  of  the  eye  in  all  its  stages  of 
development  have  been  regarded  by  some  investigators  as  almost 
insurmountable ;  2.  The  extreme  complexity  of  the  mammalian  eye, 
its  very  rapid  development,  especially  in  early  embryonic  life,  the 
appearance  and  disappearance  of  an  intricate  vascular  system  in  the 
course  of  development  with  its  concomitant  radical  changes — all 
this  obscures  the  origin  and  growth  of  the  vitreous  body  and  renders 
its  study  as  difficult  as  it  is  interesting.  The  vast  changes,  which 
follow  one  another  in  rapid  succession,  make  it  wellnigh  impossible 

Contribution  from  the  Biological  Laboratory  of  the  Catholic  University  of 
America,  No.  4. 

1 


448419 


l^ijK  &£y^<Jegree  of  certainty  later  developments.  The 
study  of  the  entire  embryonic  history  of  the  eye  alone  can  solve  the 
mysteries  of  the  origin,  the  development,  and  the  structure  of  the 
vitreous  body.  It  goes  without  saying  that  the  study  of  the  fully 
developed  eye  does  not  throw  much  light  upon  the  origin  and  de- 
velopment of  its  parts. 

To  attempt  a  solution  of  the  problem  by  methods  not  heretofore 
employed  in  this  matter,  is  the  purpose  of  this  work.  If  further 
justification  for  reopening  the  discussion  were  needed,  we  might 
point  to  the  not  very  creditable  fact  that,  to  our  knowledge,  no 
special  treatise  on  this  subject  exists  in  the  English  language. 

It  was  at  first  planned  to  make  this  study  comparative,  but  a 
closer  acquaintance  with  the  work  already  done  made  it  appear  more 
advisable  to  investigate  the  development  of  the  vitreous  body  of  one 
species  from  the  earliest  beginning  to  its  adult  condition.  The 
species  that  was  finally  selected  is  the  pig,  principally  on  account  of 
the  facility  of  obtaining  a  complete  series  of  embryonic  eyes.  More 
than  one  hundred  and  fifty  specimens,  representing  all  stages  of 
development,  were  examined.  The  material  was  obtained  from  the 
local  abattoir.  A  few  specimens  were  given  me  by  my  former 
teacher,  Dr.  Carl  R.  Moore,  of  the  University  of  Chicago,  to  whom 
I  extend  here  my  sincere  thanks  for  his  interest  in  the  success  of 
this  work.  Acknowledgment  of  indebtedness  is  also  made  to  Pro- 
fessor J.  B.  Parker,  Ph.  D.,  and  Mr.  G.  J.  Brilmyer,  M.  S.,  of  the 
Catholic  University  of  America,  under  whose  guidance  these  investi- 
gations were  made ;  to  Fr.  Mahan,  S.  J.,  and  Dr.  T.  T.  Job,  of  Loyola 
Medical  School,  Chicago,  who  kindly  permitted  me  the  use  of  their 
laboratory  in  the  summer  of  1920,  and  to  Fr.  Victor  Herring. 
0.  F.  M.,  for  preparing  most  of  the  sketches. 

HISTORICAL  SKETCH 

The  history  of  the  origin  of  the  vitreous  body  of  the  eye  dates 
back  to  the  year  1848,  when  H.  Scholer  submitted  to  the  University 
of  Dorpat  an  inaugural  dissertation  embodying  his  observations  on 
the  development  of  the  chick's  eye.  Scholer  was  the  first  to  notice 
that  very  early  in  the  development  of  the  chick  a  very  delicate 
tissue  of  mesoderm,  pars  systematis  cutis,  enters  the  optic  cup 
through  the  choroid  fissure.  Finding  no  other  elements  present, 
Scholer  naturally  attributed  to  this  portion  of  the  middle  germ 


layer  the  origin  of  the  vitreous  body.  Scholer,  therefore,  must 
be  credited  with  the  enunciation  of  the  theory  which  later  was  to 
be  known  as  the  Theory  of  the  Mesodermic  Origin  of  the  Vitreous 
Body. 

This  theory  became  more  generally  known  when  R.  Virchow, 
in  1852,  reviewed  Scholer  's  work,  approved  it,  and  classified  the 
vitreous  body,  which  had  always  defied  classification,  as  a  special 
kind  of  connective  tissue.  A.  v.  Kolliker,  in  1861,  also  accepted  the 
new  theory,  and  his  authority  blazed  the  way  for  Scholer 's  views, 
Which  thenceforth  dominated  biological  circles  almost  to  the  end  of 
the  last  century  and  which  find  defenders  even  now. 

While  all  these  authors  agree  as  to  the  mesodermic  origin  of  the 
vitreous  body,  they  differ  widely  in  determining  more  precisely 
the  portion  of  the  mesoblast  genetically  responsible  for  this  tissue. 
Most  of  them,  following  Scholer,  derive  the  vitreous  body  from 
the  mesoderm  entering  the  optic  cup  through  the  choroid  fissure. 
This  view  seems  to  be  based  largely  on  the  observations  made  in  the 
development  of  the  chick's  eye,  in  which  other  mesoblastic  elements 
are  very  scarce.  Other  investigators  have  called  attention  to  the 
relatively  large  circular  opening  between  the  lens  and  the  inner 
layer  of  the  retina  and  the  continuity  of  the  extra-ocular  mesen- 
chyme  with  the  vitreous  body.  Thus  Van  Pee  attributes  the  origin 
of  a  portion  of  the  vitreous  fibers  to  the  mesenchyme  surrounding  the 
optic  cup  on  all  sides  and  entering  through  the  perilenticular  open- 
ing. But  the  most  conflicting  statements  are  made  by  the  defend- 
ers of  the  mesodermic  origin  regarding  the  very  thin  layer  of  mesen- 
chyme originally  found  between  the  optic  vesicle  and  the  body  ecto- 
derm. Kolliker  at  first  thought  it  probable  that  during  the  forma- 
tion of  the  lens  a  part  of  this  mesoderm  is  carried  into  the  optic 
cup  and  gives  rise  to  the  tunica  vasculosa  lentis.  Later,  however, 
he  began  to  doubt  the  correctness  of  this  view.  Arnold  is  more  em- 
phatic in  attributing  the  origin  of  the  vitreous  body  exclusively  to 
this  portion  of  the  mesoderm.  On  the  other  hand,  Cirincione,  the 
most  ardent  defender  of  the  mesodermic  origin  of  the  vitreous 
body,  rejects  these  explanations  and  returns  to  Scholer 's  more  gen- 
erally accepted  views. 

The  first  to  challenge  the  theory  of  the  mesodermic  origin  of  the 
vitreous  body  was  L.  Kessler,  who,  in  1871,  made  an  exhaustive  study 
of  the  development  of  the  chick's  eye,  and  came  to  the  conclusion 
that  the  vitreous  body  is  an  amorphous  gelatinous  mass,  formed  as 


4 

an  exudation  from  the  blood  vessels,  into  which  a  few  migratory 
cells  or  leucocytes  had  found  their  way.  The  theory  of  Kessler, 
known  as  the  Transudation  Theory,  found  little  favor  with  sci- 
entists. 

A  more  generous  reception  was  accorded  to  a  new  theory  pro- 
posed by  Tornatola  at  the  International  Congress  of  Anatomists, 
held  in  Moscow,  in  1897.  Tornatola  asserted  that  the  vitreous  body 
in  vertebrates  is  essentially  a  fibrous  substance,  derived  exclusively 
from  the  retinal  cells,  and  hence  an  ectodermal  formation.  His 
Theory  of  the  Ectodermic  Origin  of  the  Vitreous  Body  found  many 
defenders,  such  as  Rabl,  Fischel,  Addario,  Wolf  rum,  v.  Szily,  Mavas, 
Magitot,  Seefelder,  and  others.  According  to  this  theory,  the 
structural  parts  of  the  vitreous  body  consist  of  a  network  of  very 
delicate  fibers,  that  have  their  origin  in  the  supporting  cells  of  the 
retina  and  hence  are  ectodermal.  The  mesoderm  elements  are 
thought  to  be  either  leucocytes  or  true  mesoderm  cells,  having, 
however,  only  vaso-formative  or  nutritive  functions  and  in  no  way 
contributing  to  the  production  of  the  vitreous  body. 

Lenhossek,  in  1902,  while  admitting  the  ectodermic  origin  of  the 
vitreous  body,  attributed  it  exclusively  to  the  lens  cells  and  pro- 
posed his  Theory  of  the  Lenticular  Origin  of  the  Vitreous  Body. 

To  reconcile  these  conflicting  opinions,  Van  Pee  and  v.  Kolliker 
almost  simultaneously  expressed  the  view  that  the  fibrous  portions 
of  the  vitreous  body  must  be  regarded  as  a  complex  tissue,  to  which 
both  ectoderm  and  mesoderm  contribute.  According  to  both  these 
investigators,  some  of  the  vitreous  fibers  originate  from  the  cells 
of  the  retina,  while  the  rest  are  the  product  either  of  the  extra-ocular 
mesenchyme  (Van  Pee)  or  of  the  extensive  vascular  system  which  is 
found  at  certain  stages  in  the  development  of  all  mammalian  eyes 
(Kolliker). 

METHODS 

The  extreme  delicacy  of  the  structure  of  the  vitreous  body  makes 
the  question  of  method  all-important.  Indeed,  diversity  of  opinion 
regarding  the  origin,  the  development,  and  the  structure  of  this 
tissue  is  owing,  in  large  measure,  to  the  methods  used. 

In  the  earlier  stages  of  development,  including  embryos  of  25 
mm  length,  most  of  the  ordinary  killing  fluids  were  found  service- 
able, Zenker's,  Bouin's,  and  Schaffner's  being  most  frequently  used. 


The  embryos  were  removed  from  the  uterus  and  immediately  placed 
into  the  killing  fluid,  which  had  been  warmed  to  about  body  tempera- 
ture. Smaller  embryos  were  fixed  in  toto ;  in  larger  specimens  the 
head  was  removed  and  sometimes  cut  longitudinally  to  permit  uni- 
form penetration.  The  material  was  left  in  the  fluids  at  least 
twenty-four  hours.  Dehydration  was  effected  by  means  of  alcohoi. 
the  material  being  passed  through  the  usual  grades  of  25%,  35%, 
etc.,  to  absolute  alcohol.  It  was  then  cleared  in  xylol  or  cedar  oil, 
the  latter  being  preferred,  because  it  clears  readily  from  95%  alco- 
hol and  because  it  prevents  the-  tissues  from  becoming  too  brittle. 
After  being  cleared,  the  tissue  was  embedded  in  paraffin.  Sections 
were  cut  in  various  thicknesses,  6,  8,  10,  15,  and  25  microns.  For 
the  study  of  the  fibrous  parts  of  the  vitreous  body,  thick  sections  are 
generally  to  be  preferred.  A  number  of  sections  were  mounted 
without  the  aid  of  a  fixative  to  eliminate,  as  far  as  possible,  all  for- 
eign material  from  the  sections,  a  perfectly  clean  slide  and  careful 
handling  being  necessary  to  bring  about  the  desired  results.  The 
fibers  of  the  vitreous  body  are  susceptible  of  almost  all  stains. 
Good  results  were  obtained  with  fuchsin,  borax-carmine,  Mallory's 
connective  tissue  stain,  Delafield's  haematoxylin,  Heidenhain's  iron- 
alum-haematoxylin  with  or  without  an  additional  slight  stain  of 
eosin  or  erythrosin.  Overstaining  was  resorted  to  in  a  few  cases 
to  bring  out  the  finer  connections  between  the  fibers.  A  heavy  stain 
greatly  facilitates  the  study  of  this  delicate  tissue.  No  material 
was  stained  in  bulk,  thus  insuring  a  uniform  stain. 

This  method  was  found  unsuited  to  embryos  of  more  than  35  mm. 
The  action  of  the  alcohol  used  in  dehydration,  and  the  heat  neces- 
sary for  paraffin  embedding  caused  greater  or  smaller  shrinkage 
of  the  vitreous  fibers,  while  the  subsequent  removal  of  the  paraffin 
almost  invariably  led  to  a  collapse  of  the  delicate  fibrous  frame- 
work of  the  vitreous  body.  For  larger  embryos  a  new  method,  first 
described  by  Szent-Gyorgyi,  with  some  modifications,  was  found  to 
give  excellent  results. 

As  killing  and  fixing  fluid  the  following  mixture  was  used : 
acetone  125  cc,  formalin  40  cc,  acetic  acid  5  cc,  water  100  cc,  mer- 
curic chloride  4  g.  The  eyes  were  carefully  removed  from  their 
sockets,  freed  of  all  adhering  tissue,  plunged  into  the  killing  fluid, 
which  had  been  heated  to  body  temperature,  and  left  in  the  fluid 
from  five  to  seven  days,  according  to  their  size.  Then  to  every  100 
cc  of  the  fluid  50  cc  of  concentrated  acetone  were  added  and  the  eyes 


left  for  an  additional  two  to  four  days.  Without  being  washed, 
they  were  then  transferred  to  concentrated  acetone  for  two  to  three 
days.  To  facilitate  dehydration,  a  layer  of  calcium  chloride  was 
spread  in  the  bottom  of  the  vessel.  To  prevent  a  too  violent  action 
of  the  calcium  chloride  on  the  eyes,  direct  contact  between  the  two 
must  be  avoided.  The  material  was  then  placed  for  twenty-four 
hours  in  ether-alcohol,  and  thereafter  embedded.  Embedding  was 
done  in  celloidin  or  paralodion,  dissolved  in  ether-alcohol,  smaller 
eyes  being  placed  successively  in  2,  5,  8,  and  10%  solution,  larger 
eyes  in  1,  3,  5,  and  8%  solution,  remaining  in  each  about  three  days. 
Parts  of  the  coats  of  the  eyes  were  removed  before  embedding  to 
insure  perfect  penetration.  Hardening  was  done  by  means  of 
chloroform  and  terpineol.  Sections  were  cut  very  thick,  100,  150, 
200,  250,  and  300  microns.  They  were  placed  into  a  95%  alcoholic 
solution  of  iodin  to  remove  the  mercuric  chloride  crystals,  then  into 
75%  alcohol  and,  immediately  before  staining,  into  distilled  water. 
Various  stains  were  tried,  the  best  results  being  obtained  with 
Held's  molybdic  haematoxylin  (haematox.  cryst.  1  g.,  molybdic 
acid  10  g.,  70%  alcohol  100  cc).  The  stain  was  permitted  to  ripen 
about  three  weeks,  carefully  decanted  and,  before  use,  diluted  with 
ten  times  its  volume  of  distilled  water.  The  sections  were  then 
passed  through  the  various  grades  of  alcohol  to  95%,  cleared  in 
carbol-xylol,  and  mounted  in  balsam.  The  structure  and  arrange- 
ment of  the  fibrous  part  of  the  vitreous  body  were  brought  out  with 
remarkable  clearness  in  this  way,  but,  unfortunately,  the  remain- 
ing structures  were  deeply  overstained.  To  remedy  this  defect, 
some  sections  were  stained  in  Lyons  Blue,  but  with  indifferent 
success. 

INVESTIGATION 

I     PRIMITIVE  VITREOUS  BODY 

The  period  of  development  forming  the  object  of  this  part  of 
our  investigation,  includes  embryos  ranging  from  4  to  11  mm  in 
length  and  shows  the  origin  and  growth  of  the  eye  from  its  begin- 
ning to  the  completion  of  the  optic  cup  and  the  lens  vesicle,  before 
the  appearance  of  blood  vessels  in  the  cavity  of  the  vitreous  body. 
It  shows  the  latter  in  its  primitive  and  simplest  form,  not  obscured 
by  the  numerous  mesodermal  elements,  which  later  render  its  study 
more  difficult. 


In  embryos  of  4,  5,  and  6  mm,  we  witness  the  origin  of  the  eye. 
The  primary  optic  vesicle  gradually  invaginates  to  form  the  optic 
cup,  the  overlying  body  ectoderm  thickens  and  bends  inward  to  give 
rise  to  the  lens  vesicle.  Cup  and  lens  are  in  close  contact  through- 
out; no  mesoderm  is  found  between  them  (Figure  6).  The  cavity 
of  the  vitreous  body,  the  posterior  chamber  of  the  eye,  is  absent  in 
the  younger  specimens,  but  appears  as  a  narrow  slit  between  future 
retina  and  lens  in  the  6  mm  embryo.  The  development  thenceforth 
is  very  rapid,  and  in  the  11  mm  embryo,  the  structure  of  the  eye 
may  be  described  thus :  the  optic  cup  is  complete,  consisting  of  an 
inner  layer,  the  retina,  and  an  outer,  the  pigment  layer.  The  former 
shows  two  distinct  regions,  a  cellular,  and  the  so-called  mantle  layer. 
Nerve  fibers  and  pigment  are  still  absent.  The  lens  vesicle  has  sepa- 
rated from  the  body  ectoderm.  The  choroid  fissure  is  wide  open, 
and  the  surrounding  mesoderm  is  pressing  up  into  the  fissure  (Fig- 
ure 3),  but  has  not  yet  penetrated  into  the  optic  cup.  The  optic 
stalk,  an  open  tube  with  wide  lumen,  can  easily  be  traced  to  the 
diencephalon. 

The  cavity  of  the  vitreous  body  is  still  narrow.  It  contains  no 
blood  vessels  and  only  a  few  cells  scattered  here  and  there.  The 
origin  and  the  nature  of  these  cells  have  not  been  satisfactorily  ex- 
plained. Some  authors,  as  v.  Lenhossek,  consider  them  the  rem- 
nants of  the  thin  layer  of  mesoderm  originally  found  between  the 
optic  vesicle  and  the  body  ectoderm,  and  carried  into  the  optic  cup 
by  the  invaginating  lens  placode.  Others,  among  whom  are  See- 
felder,  Mavas,  and  Magitot,  maintain  that  these  cells  have  migrated 
from  the  retinal  mantle  layer  into  the  vitreous  body.  Seefelder 
proposes  to  call  them  ectodermal  vitreous  body  cells  (ektodermale 
Glasskorperzellen),  and  believes  them  to  be  identical  with  similar 
cells  found  later  in  large  numbers  in  the  mantle  layer  of  the  retina. 
Mavas  and  Magitot,  moreover,  are  of  opinion  that,  passing  through 
a  process  of  degeneration  and  disintegration,  these  cells  contribute 
to  the  production  of  the  liquid  parts  of  the  vitreous  body.  Wolf  rum 
believes  some  to  be  real  mesoderm  cells  with  vaso-formative  function, 
others  he  prefers  to  call  ectodermal  cells.  The  difference  of  opinion 
may,  to  some  extent,  be  owing  to  the  difference  in  the  material  used. 
In  the  material  which  formed  the  subject  of  our  investigation,  the 
cellular  elements  are  exceedingly  rare,  scarcely  half  a  dozen  being 
counted  in  as  many  complete  series  of  sections.  In  the  eye  of  the 
pig,  in  which  no  mesoderm  is  carried  into  the  optic  cup  by  the  lens 


8 

placode  (Figure  6),  and  in  which  at  this  time  no  mesoderm  has 
entered  through  the  choroid  fissure  (Figure  1),  it  would  be  difficult 
to  account  for  the  presence  of  mesoderm  in  the  vitreous  body. 
In  structure,  the  cells  resemble  the  retinal  cells.  For  these 
reasons,  we  incline  to  the  belief,  that  they  are  of  retinal  origin  and 
not  mesenchyme.  But  whatever  their  origin  and  their  nature  may 
be,  they  show  no  connection  with  the  vitreous  body,  nor  do  they  at 
this  stage  of  development  contribute  to  the  production  of  the  vitre- 
ous fibers. 

The  vitreous  body  is  represented  in  all  embryos  by  a  great  mass 
of  fibers,  of  which  the  larger  portion  extend  radially  between  the 
retina  and  the  lens,  while,  especially  in  embryos  of  10  and  11  mm, 
some  very  prominent  fibers  are  seen  running  approximately  parallel 
to  the  retina  and  lens.  It  is  not  difficult  to  determine  the  origin  of 
both.  The  radial  fibers  arise  as  long  slender  outgrowths  from  the 
conelike  bases  of  the  inner  layer  of  retinal  cells  (Miiller's  support- 
ing cells).  Some  can  be  traced  directly  from  the  retina  to  the  lens, 
others  are  seen  to  send  off  branches  in  various  directions  which, 
dividing  and  subdividing,  anastomose  freely  with  branches  from 
neighboring  fibers,  forming  a  dense  reticulum  in  which  further 
tracing  becomes  impossible.  The  fibers  are  slightly  granular  and 
react  to  the  various  stains  in  a  manner  not  unlike  that  of  the 
cytoplasm  of  their  mother  cells.  In  some  sections,  larger  granules 
are  found  at  the  junction  or  branching  points  of  the  fibers,  but  their 
absence  in  the  more  perfect  preparations,  especially  in  the  celloidin 
preparations,  seems  to  show  them  to  be  artefacts,  produced  by 
precipitation.  In  the  more  perfect  sections,  the  fibers  appear  almost 
homogeneous,  slightly  granular,  tapering  gradually  from  their 
broad  bases  at  the  retina  to  a  slender  thread  near  the  lens.  In  the 
narrow  isthmus  between  the  anterior  part  of  the  retina  and  the 
lens,  a  very  regular  structure  of  the  fibers  is  frequently  found. 

The  radial  fibers,  however,  are  not  restricted  to  the  retina;  the 
basal  cells  of  the  lens  also  send  out  a  large  number  of  them.  These 
fibers  differ  widely  from  the  retinal  fibers.  They  are  short  and 
never  traceable  to  the  retina.  At  a  short  distance  from  the  lens, 
they  split  into  several  branches  which  run  almost  parallel  to  the 
posterior  part  of  the  lens.  At  this  point  they  are  met  by  the  more 
numerous  and  more  massive  retinal  fibers,  and  together  with  them 
they  form  a  thick,  feltlike  mass,  especially  observable  in  equatorial 
sections  (Figures  1  and  8).  The  entire  surface  of  the  lens  con- 


9 

tributes  to  the  formation  of  these  fibers,  especially  the  cells  oppo- 
site the  region  where  retina  and  pigment  layer  meet.  On  the  ante- 
rior surface  of  the  lens,  some  of  these  fibers  penetrate  deeply  into 
the  surrounding  mesoderm  with  which  they  frequently  unite ;  others 
even  find  their  way  to  the  overlying  body  ectoderm.  In  the  more 
advanced  stages  of  development,  when  the  lens  capsule  begins  to  be 
formed  as  a  secretion  of  the  lens  cells,  the  lenticular  fibers  gradually 
lose  their  connection  with  the  basal  cells  of  the  lens.  The  light 
space  between  the  lens  and  the  feltlike  mass  of  fibers  described  above 
(Figure  1)  signalizes  the  region  of  the  future  tunica  vasculosa 
lent-is,  or  vascular  capsule  of  the  lens. 

The  vitreous  body  at  this  stage  of  development,  therefore,  con- 
sists of  fibers,  both  radial  and  parallel,  which,  springing  from  the 
conelike  projections  of  the  basal  cells  of  the  retina  and  lens,  form 
with  frequent  anastomoses  a  dense  network,  or  rather  framework, 
constituting  the  solid  or  structural  part  of  the  vitreous  body.  These 
fibers  arise  solely  as  protoplasmic  prolongations  of  the  retinal  and 
lenticular  cells  and  are,  therefore,  ectodermal  in  their  origin.  No 
mesodermal  elements  contribute  to  their  production. 

We  can  not  agree,  therefore,  with  Scholer  and  his  followers  in 
their  contention,  that  the  vitreous  body  takes  its  origin  from  the 
mesoderm  entering  through  the  choroid  fissure ;  for  in  all  embryos, 
examined  at  the  various  stages  of  development  up  to  12  mm  length, 
no  mesoderm  was  found  to  have  entered  into  the  optic  cup  through 
the  choroid  fissure.  The  cells  found  here  and  there  in  the  vitreous 
body,  whatever  their  origin,  nature,  and  ultimate  fate  may  be,  take 
no  part  in  the  production  of  the  primitive  vitreous  body  fibers,  nor 
do  they,  at  this  stage,  enter  into  any  connection  with  them.  The 
fibers  can  be  traced  so  easily  to  the  basal  cells  of  the  retina  and 
lens  that  their  retinal  and  lenticular  origin  respectively,  at  this 
stage  of  the  development  of  the  eye,  admits  of  no  doubt. 

Cirincione  maintains  that  these  fibers  are  only  temporary,  and 
that  their  sole  purpose  is  to  fill  out  the  cavity  of  the  optic  cup  until 
the  permanent  vitreous  body  is  formed  by  the  mesoderm  entering 
later  through  the  choroid  fissure.  He  admits  the  presence  of  the 
retinal  and  the  lenticular  fibers,  and  concedes  their  origin  from  the 
basal  cells  of  the  retina  and  lens,  but  regards  them  only  as  a 
sostanza  di  replezione  destined  to  disappear  in  the  same  degree  as 
the  mesodermal  elements  advance  into  the  cavity  of  the  secondary 
optic  vesicle  to  form  the  vitreous  body  (page  1,358).  But  further 


10 

investigation  will  show  that  this  primitive  condition  of  the  vitreous 
body,  although  obscured  and  modified  by  the  ingrowing  mesoderm, 
remains  essentially  the  same.  A  comparison  of  figures  2  and  19 
shows  rather  that  the  mesodermal  elements  are  only  temporary 
structures  in  the  vitreous  body,  which  both  in  its  primitive  and  in 
its  final  stage  of  development  is  purely  ectodermal. 

Neither  do  our  observations  agree  with  the  views  of  Kessler  that 
the  vitreous  body  is  an  amorphous,  gelatinous  mass,  the  product  of  a 
process  of  transudation  from  the  blood  vessels  (page  81).  Its 
fibrous  structure  is  so  uniform,  regular,  and  constant  in  all  sections, 
whatever  method  is  used  in  their  preparation,  that  we  can  not  regard 
the  vitreous  body  as  an  amorphous  mass.  To  dispose  of  the  fibers  as 
artificial  productions  of  the  reagents  used  in  the  preparation  of  the 
material,  would  be  to  do  violence  to  fact. 

By  a  careful  study  of  the  vitreous  body  in  the  sheep 's  eye,  Van 
Pee  arrives  at  the  conclusion,  that  the  radial  fibers  are,  indeed,  of 
retinal  or  ectodermal  origin,  but  that  the  more  prominent  parallel 
fibers,  which  constitute  the  bulk  of  the  vitreous  body,  are  mesodermal 
in  their  origin,  arising  from  the  mesenchyme  between  the  optic  cup 
and  the  body  wall.  These  fibers  then  pass  through  the  narrow  peri- 
lenticular  opening  and  form  the  major  part  of  the  vitreous  body. 
It  is  true,  as  will  be  seen  from  figure  2,  that  at  a  later  stage  of 
development  numerous  mesoderm  cells  with  long  protoplasmic  out- 
growths enter  into  the  vitreous  body,  and  the  significance  of  this 
formation  will  be  considered  in  its  place,  but  it  is  equally  true,  that 
in  the  earlier  stages,  which  are  under  consideration  here,  and  which 
show  the  vitreous  body  in  its  primitive  and  simplest  form,  both  the 
radial  and  the  parallel  fibers  are  exclusively  the  product  of  the  basal 
cells  of  the  retina  and  lens.  In  the  eye  of  the  pig,  mesodermal 
vitreous  fibers  are  hot  found  at  this  stage  of  development. 

Lenhossek,  in  a  lengthy  monograph,  attempts  to  demonstrate 
that  all  the  fibers  constituting  the  structural  parts  of  the  vitreous 
body,  are  the  product  of  the  basal  cells  of  the  lens,  and  that  the 
retina  has  no  share  in  their  production.  All  our  preparations  show 
the  lenticular  fibers  first  described  by  v.  Lenhossek  and  later  by  his 
pupil,  v.  Szily.  They  are  especially  prominent  in  embryos  of  10 
and  11  mm  length,  radiating  from  all  parts  of  the  lens,  and  enter- 
ing into  communication  with  the  retinal  fibers,  the  extra-ocular 
mesoderm,  and  even  with  the  body  ectoderm.  But  we  can  not  regard 
them  as  the  exclusive  structural  parts  of  the  vitreous  body.  It  is 


11 

surprising  that  v.  Lenhossek  should  have  overlooked  the  more 
numerous,  more  massive,  and  more  prominent  fibers  arising  from  the 
retina.  The  retinal  fibers,  moreover,  are  a  permanent  formation, 
as  will  appear  from  further  study;  the  lenticular  fibers  are  very 
early  separated  from  their  mother  cells  by  the  formation  of  the  lens 
capsule,  as  v.  Lenhossek  himself  points  out.  Wolfrum  is  of  the 
opinion  that  the  lenticular  fibers  serve  as  an  apparatus  for  retaining 
the  lens  vesicle  in  its  place  after  it  has  separated  from  the  body 
ectoderm.  The  peculiar  shape  of  the  lens  vesicle  at  this  time  seems 
to  lend  color  to  this  theory.  Whether  or  not  the  lens  fibers  contrib- 
ute to  the  formation  of  the  primitive  vitreous  body,  their  influence 
is  neither  predominant  over,  nor  equal  to,  that  of  the  retina,  while 
after  the  formation  of  the  lens  capsule,  no  further  connection  exists 
between  the  lens  and  the  vitreous  body.  Kolliker  says  of  v.  Len- 
hossek 's  theory :  The  lenticular  vitreous  body  of  v.  Lenhossek  does 
not  exist  (page  18). 

The  purely  retinal,  i.  e.,  ectodermal  origin  of  the  primitive 
vitreous  body,  as  described  in  this  chapter,  has  found  defenders 
in  many  modern  investigators.  It  may  suffice  to  mention  Tornatola, 
Addario,  Wolfrum,  v.  Szily,  v.  Kolliker,  Mavas,  Magitot,  and  See- 
felder.  Mavas  and  Magitot  thus  sum  up  the  results  of  their  in- 
vestigation on  the  origin  and  the  development  of  the  vitreous  body 
in  the  human  eye :  The  primitive  vitreous  body  is  of  retinal  original. 
It  consists  of  a  very  delicate  fibrous  mass,  arising  from  the  marginal 
zone  of  the  embryonic  retina.  This  marginal  layer  is  formed  by 
protoplasmic  prolongations  of  the  supporting  cells,  which  are  the 
first  to  differentiate  in  the  inner  layer  of  the  optic  vesicle.  The 
primitive  vitreous  body  is,  therefore,  an  exoplastic  formation  of  this 
layer  (page  127). 

II  PERIOD  OF  MESODERMAL  INVASION  OF  THE  VITREOUS  BODY 
The  primitive  simple  condition  of  the  vitreous  body  soon  under- 
goes a  radical  change,  brought  about  by  the  entrance  of  the  complex 
hyaloid  vascular  system  and  numerous  mesodermal  elements.  The 
relationship  of  these  structures  to  the  vitreous  body  is  of  paramount 
importance  in  judging  of  the  true  character  and  the  further  develop- 
ment of  the  latter. 

The  hyaloid  artery,  a  branch  of  the  arteria  centralis  retinae, 
entering  the  optic  cup  through  the  still  partly  open  choroid  fissure, 
at  first  appears  as  a  single  solid  trunk,  pushing  its  way  far  into  the 


12 

vitreous  body  (Figure  4).  It  soon  gives  rise  to  a  number  of  branches 
which  fill  out  the  larger  part  of  the  space  between  the  retina  and  the 
lens  (Figure  2).  Their  tendency,  however,  is  always  towards  the 
lens,  which  finally  is  completely  surrounded  by  blood  vessels  furnish- 
ing it  with  nourishment  during  the  period  of  its  most  rapid  growth. 
Later  there  arises  from  the  hyaloid  artery  near  its  entrance  into  the 
optic  cup  a  second  group  of  branches  which  radiate  in  all  directions 
through  the  outer  layer  of  the  vitreous  body  near  the  retina.  This 
condition  is  observable  especially  in  embryos  ranging  from  35  to  100 
mm  in  length  (Figure  14).  The  larger  part  of  the  vitreous  body  of 
such  embryos  is  again  free  from  blood  vessels. 

A  closer  examination  of  the  structure  of  the  blood  vessels  shows 
that  their  walls  are  generally  thin,  consisting  of  a  layer  of  endothelial 
cells  to  which  a  connective  tissue  cell  is  attached  here  and  there.  This 
structure  is  common  to  the  main  trunk  as  well  as  to  all  the  branches 
of  the  hyaloid  system  at  this  time.  Later,  however,  the  main  trunk  of 
the  hyaloid  artery  seems  to  be  surrounded  by  an  additional  layer  of 
cells  enveloping  the  vascular  endothelium  like  a  mantle.  This  mantle 
layer  has  been  classed  by  some  authors  among  the  neuroglia  tissues 
of  the  central  nervous  system.  Its  intimate  connection  with  the  sup- 
porting tissues  of  the  optic  nerve,  the  structure  and  the  epithelial  ar- 
rangement of  its  cells,  and  the  reaction  of  the  latter  to  stains  in  a 
manner  not  unlike  the  neuroglia  cells  of  the  optic  nerve,  are  said  to 
prove  the  identity  of  this  cell  layer  with  the  supporting  tissues  of  the 
optic  nerve  (Mavas  and  Magitot,  p.  129) .  For  the  eye  of  the  pig,  this 
structure  has  been  described  at  length  by  Wolf  rum  (p.  249) ,  to  whom 
the  interested  reader  is  referred. 

While  Seefelder  at  first  observed  the  neuroglia  mantle  around 
only  the  main  trunk  of  the  hyaloid  artery,  Mavas  and  Magitot  found 
it  enveloping  not  only  the  main  trunk,  but  all  the  branches  of  the 
hyaloid  system,  thus  interposing  an  ectodermal  sheath  of  neuroglia 
tissue  between  the  mesodermal  elements  of  the  blood  vessels  and 
the  vitreous  body  and  effectively  preventing  their  union.  Ac- 
cording to  these  authors,  therefore,  the  vitreous  body  is  at  this  time 
free  from  all  mesodermal  admixture,  and  represents  a  purely  ecto- 
dermal formation  consisting  of  a  framework  of  fibers,  the  product 
partly  of  the  supporting  tissues  of  the  retina  and  partly  of  the 
neuroglia  cells  of  the  optic  nerve.  The  vitreous  body  would  then 
have  to  be  regarded  as  a  purely  neuroglia  tissue  derived  ultimately 
from  the  central  nervous  system  (Mavas  and  Magitot,  p.  132). 


13 

This  simple  solution  of  the  complex  vitreous  body  problem,  how- 
ever, meets  with  some  difficulties  in  the  subject  under  consideration 
here.  The  above-mentioned  investigators  arrived  at  their  conclusion 
by  the  study  of  human  material  almost  exclusively.  But  in  the  eye 
of  the  pig,  the  neuroglia  mantle  has  been  observed  around  only 
about  one-third  of  the  length  of  the  main  trunk  of  the  hyaloid  ar- 
tery ;  it  has  never  been  shown  to  surround  any  of  its  branches.  Our 
own  observations  agree  fully  with  those  of  Wolfrum.  A  number 
of  sections  show  the  neuroglia  mantle  surrounding  a  portion  of  the 
hyaloid  artery  proper ;  but  the  branches  exhibit  only  the  usual  vas- 
cular endothelium,  which,  as  further  investigation  will  show,  enters 
into  a  close  relationship  with  the  vitreous  body.  This  complex 
relationship  between  the  vitreous  body  and  the  mesodermal  ele- 
ments of  the  blood  vessels  prevents  our  accepting,  for  the  eye  of 
the  pig  at  least,  the  simple  and  attractive  theory  of  the  neuroglia 
origin  and  nature  of  the  vitreous  body. 

But  there  are  other  elements  found  in  the  optic  cup  at  this  time 
of  development  which  claim  our  attention.  Together  with  the  hyaloid 
artery,  some  free  mesoderm  cells  likewise  enter  the  optic  cup 
and  almost  simultaneously  we  witness  the  invasion  of  the 
vitreous  body  by  a  large  mass  of  mesoderm  through  the  perilenticu- 
lar  opening  (Figure  2).  The  function  of  these  mesodermal  ele- 
ments has  never  been  satisfactorily  accounted  for.  Several  cir- 
cumstances, to  which,  as  far  as  we  know,  attention  has  not  yet  been 
called,  incline  us  to  the  belief  that  these  mesoderm  cells  are  pri- 
marily vaso-formative,  aiding  in  the  building  up  of  the  complex 
vascular  system  of  the  embryonic  mammalian  eye :  1.  the  invasion 
of  the  vitreous  body  by  mesoderm  is  restricted  to  a  comparatively 
short  period  of  time,  which  corresponds  to  the  period  of  the  most 
rapid  growth  and  expansion  of  the  vascular  system,  and  ceases  as 
soon  as  the  latter  has  attained  its  highest  development  (Figures  2 
and  12)  ;  2.  while  at  first  the  mesodermal  elements  are  found  scat- 
tered throughout  the  larger  part  of  the  vitreous  body,  most  of  them 
soon  congregate  in  the  vicinity  of  the  blood  vessels,  the  rest  of  the 
vitreous  body  being  at  that  time  almost  devoid  of  mesoderm ;  3.  that 
there  exists  some  relationship  between  the  vascular  system  of  the 
vitreous  body  and  the  mesodermal  elements,  seems  to  be  indicated 
also  by  the  fact  that  in  the  eye  of  the  birds,  which  even  during  em- 
bryonic development  never  contains  blood  vessels,  the  number  of 
mesoderm  cells  is  exceedingly  small.  Many  authors  even  doubt  the 


14 

presence  of  mesoderm  in  the  chick's  eye.  Lillie  says  of  these  cells 
that  "in  character  they  resemble  embryonic  blood-cells  and  not 
mesenchyme,  and  disappear  entirely  by  the  eighth  day"  (p.  275). 

That  not  all  the  mesoderm  cells  are,  however,  used  in  the  forma- 
tion of  the  blood  vessels  is  evident  from  the  fact  that  at  all  stages 
of  development  a  number  of  them  are  found  isolated  in  the  vitreous 
body.  It  is  not  improbable,  as  some  authors  maintain,  that  these 
free  mesoderm  cells  by  a  process  of  disintegration  and  degeneration 
contribute  to  the  production  of  the  fluid  parts  of  the  vitreous  body. 
Accordingly,  we  have  at  this  period  of  development  two  distinct 
mesodermal  elements  in  the  vitreous  body,  the  mesoderm  tissue  of 
the  blood  vessels  and  a  number  of  free  mesoderm  cells  (Figure  13). 

The  question  now  arises  as  to  what  influence  the  hyaloid  system 
and  the  free  mesoderm  cells  have  on  the  further  development  of 
the  vitreous  body.  Do  they  modify  the  originally  ectodermal  nature 
of  this  tissue  in  such  wise  that  we  are  forced  to  admit  a  mixed  struc- 
ture consisting  of  various  parts,  derivatives  of  both  the  outer  and 
the  middle  germ  layer  ? 

It  can  not  be  denied  that  a  close  relationship  arises  between  the 
fibers  of  the  vitreous  body  and  the  walls  of  the  blood  vessels.  The 
endothelium  of  the  latter  sends  out  a  large  number  of  fibers  which 
penetrate  into  the  surrounding  vitreous  body.  They  are  short  and 
delicate  and  never  attain  the  massiveness  of  the  vitreous  fibers. 
Their  purpose  may  be  solely  to  secure  a  hold  for  the  blood  vessels 
in  the  loose  surrounding  tissue,  a  phenomenon  not  infrequently 
observed  in  embryonic  structures.  The  retinal  fibers,  on  the  other 
hand,  enter  into  direct  union  with  the  blood  vessels.  It  is  not  diffi- 
cult to  trace  many  fibers  in  their  entire  course  from  the  retina  to  the 
endothelial  lining  of  the  blood  vessels,  forming  a  protoplasmic 
bridge  between  the  two.  While  the  phenomenon  can  be  observed 
at  almost  any  stage  of  development,  it  is  especially  prominent  in 
embryos  ranging  from  50  to  130  mm  in  length.  Here  at  times  we 
see  the 'fibers  apparently  radiating  from  the  blood  vessels  like  the 
radii  of  a  wheel  (Figure  14).  It  is  probable  that  in  this  way  nutri- 
ment is  carried  from  the  blood  vessels  to  the  vitreous  body  and  also 
to  the'  retina,  which  for  a  long  time  is  deprived  of  a  vascular  system 
of  its  own. 

A.  v.  Szily,  who  has  devoted  much  labor  to  the  study  of  this 
peculiar  phenomenon  of  the  concrescence  of  ectodermal  vitreous 


15 

body  fibers  and  mesodermal  endothelial  cells,  maintains  that  the 
retinal  fibers  after  entering  into  a  union  with  the  mesoderm,  lose 
all  connection  with  their  mother  cells  of  the  retina,  and  become 
structurally  as  well  as  functionally  dependent  on  the  endothelium 
of  the  blood  vessels.  We  should  thus  have  the  unique  case  of  an 
ectodermal  structure  separating  from  its  parental  tissue  and  enter- 
ing into  functional  dependence  on  a  mesodermal  structure,  a  phe- 
nomenon unparalleled  in  embryonic  development.  While  it  is  true, 
that  in  the  inner  portions  of  the  optic  cup,  with  progressive  differ- 
entiation, the  retina  loses  the  faculty  of  producing  vitreous  fibers, 
this  does  not  hold  of  the  retina  in  its  whole  extent.  In  embryos  of 
25  and  even  35  mm  length,  which  marks  the  height  of  development 
of  the  vascular  system,  the  greater  part  of  the  vitreous  fibers  is  still 
in  connection  with  the  retina,  while  throughout  the  whole  course 
of  embryonic  development,  and  even  in  the  fully  developed  eye, 
the  vitreous  body  fibers  remain  united  with  the  retina  in  the  region 
of  the  pars  ciliaris  sive  coeca  retinae.  There  the  vitreous  body  never 
separates  from  the  basal  cells  of  the  retina  to  which  it  owes  its  ori- 
gin. This  may  be  readily  seen  by  comparing  the  corresponding 
sections  of  the  eyes  of  embryos  of  25,  35,  60,  80,  100,  130,  175,  and 
250  mm  length.  As  the  study  of  this  part  of  the  retina,  at  various 
stages  of  development,  throws  much  light  on  the  development  and 
the  ultimate  structure  of  the  vitreous  body,  we  have  reproduced  a 
number  of  these  both  by  sketches  and  by  photographs.  A 
close  study  of  these  also  refutes  the  theory  of  v.  Lenhossek  that  the 
vitreous  body,  separating  from  its  place  of  origin,  the  basal  cells  of 
the  crystalline  lens,  forms  a  syncytium,  deprived  of  cellular  ele- 
ments, and  capable  of  independent  growth,  development,  and  nutri- 
tion. Even  in  those  regions  where  the  retina  loses  the  faculty  of 
producing  vitreous  fibers,  there  is  no  clear  separation  between  the 
two.  The  vitreous  body  even  there  retains  its  intimate  connection 
with  the  internal  limiting  membrane  of  the  retina  by  a  great  number 
of  very  delicate  fibrils,  which  form  the  ragged  edge  of  the  vitreous 
body  in  sections  where  shrinkage  has  pulled  the  two  apart. 

That  the  vitreous  body  fibers  also  enter  into  close  relationship 
with  the  free  mesodermal  elements  found  in  the  vitreous  body  is 
made  clear  by  many  sections.  After  the  manner  of  embryonic  con- 
nective tissue  cells,  many  of  the  mesoderm  cells  assume  a  stellate 
or  fusiform  shape  and  send  out  protoplasmic  processes  of  greater  or 
shorter  length.  From  these  not  infrequently  long  slender  threads 


16 

arise  which  attach  themselves  to  any  structure  within  reach,  whether 
other  mesoderm  cells  or  blood  vessels  or  vitreous  body  fibers.  There 
seems  to  be  no  doubt  that  the  latter  also  enter  into  direct  union  with 
the  mesoderm  cells.  We  have  thus  an  extremely  complex  relation- 
ship between  retinal  fibers,  blood  vessels  and  free  mesoderm  cells. 
We  would  emphasize  this  fact  in  view  of  the  contention  of  Mavas, 
Magitot,  and  Seefelder,  that  the  mesodermal  elements  present  in  the 
vitreous  body  are  hermetically  shut  off  (Seefelder)  from  the  latter, 
thus  excluding  the  possibility  of  mesodermal  contributions  to  the 
vitreous  body. 

In  view  of  the  complex  relationship  between  ectodermal  and 
mesodermal  elements  in  the  vitreous  body,  we  agree  with  v.  Szily 
that  the  "vitreous  body  problem"  is  not  so  much  to  decide  its  ori- 
gin, which  at  the  present  time  is  almost  universally  regarded  as 
ectodermal,  but  to  determine  the  influence  of  various  mesodermal 
structures  upon  its  further  development.  Szily  puts  the  question 
on  a  wider  basis  in  so  far  as  he  maintains  the  real  point  at  issue  is 
the  union  of  two  structures,  primarily  derived  from  different  germ 
layers,  into  one  tissue.  While  all  our  preparations  of  many  stages 
of  development  of  the  eye  of  the  pig,  reveal  this  complex  union 
of  mesodermal  and  ectodermal  derivatives  in  a  clear  and  unmis- 
takable manner,  we  are  not  prepared  to  follow  v.  Szily  in  asserting 
that  the  ectodermal  vitreous  body  fibers  become  also  functionally 
dependent  on  the  mesoderm.  It  is  the  retina  which  gives  rise  to  the 
primitive  vitreous  body ;  it  is  the  retina  which  directs  and  controls 
the  development  of  its  structural  parts ;  it  is  the  retina  which  in  the 
fully  developed  eye  contributes  exclusively  to  the  formation  of  the 
vitreous  body.  The  retina  alone  never  loses  its  original  relationship 
to  the  vitreous  fibers;  upon  the  retina  they  are  structurally  and 
functionally  dependent  in  their  origin,  development,  and  final  ar- 
rangement. Though  this  intimate  relationship  between  retina  and 
vitreous  body  is  found  at  first  in  the  whole  extent  of  the  retina,  it  is, 
however,  later  restricted  to  a  narrow  circular  strip  of  the  retina 
between  the  ora  serrata  and  the  pars  ciliaris  retinae  proper.  There 
the  controlling  influence  of  the  retina  upon  the  vitreous  body  fibers 
is  manifest  at  every  stage  of  development  as  well  as  in  the  eye  of 
the  adult  animal. 

Our  conception  of  the  relationship  between  retina  and  vitreous 
body  finds  a  singular  confirmation  in  the  results  of  experiments 
made  by  Haemers  to  determine  whether  regeneration  of  the  vitreous 


17 

body  is  possible  and  how  it  takes  place.  After  a  number  of  experi- 
ments on  the  eyes  of  various  animals,  Haemers  asserts  that  ''the 
vitreous  body  regenerates  at  the  expense  of  the  retinal  neuroglia" 
(page  114) .  But  surely,  the  regeneration  of  one  tissue  from  another 
presupposes  a  relationship  of  dependence  between  them.  It  is  to 
be. regretted  that  Haemers  has  not  found  any  followers  in  his  in- 
genious attack  upon  the  vitreous  body  problem  by  a  careful  study  of 
the  process  of  regeneration.  No  doubt,  a  repetition  and  extension  of 
Haemers'  investigations  would  tend  to  clear  up  other  difficulties 
and  point  the  way  for  a  final  solution  of  this  interesting  and  difficult 
problem.  Regeneration  of  the  vitreous  body  has  been  observed  also 
by  Sauri. 

During  the  period  of  development  described  in  this  chapter, 
the  general  appearance  of  the  vitreous  body  has  greatly  changed 
even  in  the  regions  not  directly  affected  by  the  invasion  of  the  meso- 
derm.  While  during  the  earlier  stages,  including  embryos  of  35  mm 
length,  the  radial  fibers  still  form  the  larger  part  of  its  structure, 
we  soon  observe  that  they  are  more  and  more  replaced  by  fibers  run- 
ning approximately  parallel  to  retina  and  lens.  The  parallel  fibers 
are  at  first  found  in  the  exterior  regions  of  the  vitreous  body  near 
the  retina,  where  they  gradually  assume  the  appearance  of  a  special 
membrane,  distinct  from  the  internal  limiting  membrane  of  the 
retina,  and  forming  the  outer  covering  of  the  vitreous  body.  It  has 
been  generally  called  the  hyaloid  membrane.  Later  a  number  of 
fibers  are  found  to  take  their  course  from  the  region  anterior  to  the 
ora  serrata  to  the  posterior  part  of  the  lens  and  then  turn  inward 
in  the  direction  of  the  optic  nerve.  They  represent  the  first  traces 
of  a  more  solid  portion  of  the  anterior  surface  of  the  vitreous  body, 
and  they  have  sometimes  been  called  the  anterior  hyaloid  membrane. 
The  discussion  of  the  significance  of  these  structures  will  be  reserved 
for  the  next  chapter. 

Our  conclusions,  derived  from  the  study  of  this  most  important 
period  in  the  development  of  the  vitreous  body,  may  be  summed  up 
thus:  The  original  purely  ectodermal  structure  of  the  vitreous 
body  is  radically  changed  by  the  accession  of  various  mesodermal 
elements  in  the  form  of  blood  vessels  and  free  mesoderm  cells  with 
their  outgrowths.  The  ectodermal  vitreous  fibers  enter  into  a  close 
relationship  with  the  mesoderm,  the  relationship  being  one  not  only 
of  contiguity  but  of  protoplasmic  continuity,  consisting  of  a  pro- 
topi  •j^mic  union  between  them.  This  union,  however,  does  not  de- 


18 

prive  the  retina  of  its  controlling  influence  in  the  further  develop- 
ment of  the  vitreous  body,  which  throughout  remains  functionally 
dependent  on  it.  The  vitreous  body,  therefore,  at  this  stage  of  de- 
velopment is  a  very  complex  structure,  the  constituent  parts  of 
which  are  partly  ectodermal  and  partly  mesodermal  in  their  origin. 

• 
III     THE  PERMANENT  VITREOUS  BODY 

The  structure  of  -the  vitreous  body  described  in  the  preceding 
chapter,  is  not  a  permanent  one.  The  hyaloid  vascular  system,  hav- 
ing fulfilled  its  function  of  supplying  nourishment  to  the  crystalline 
lens,  soon  shows  signs  of  degeneration  and  gradually  disappears. 
The  remnants  of  the  mesodermal  cells  begin  to  disintegrate  and 
dissolve.  The  vitreous  body  then  appears  again  in  its  original 
purity,  modified  indeed  and  greatly  changed,  but  in  its  essentials 
like  the  primitive  ectodermal  vitreous  body.  An  excellent  repre- 
sentation of  its  general  appearance  and  internal  structure  is  found 
on  plate  VI,  showing  various  portions  of  the  eye  of  a  fetus  220  mm 
in  length. 

Figure  17  represents .  a  horizontal  section  of  the  eye,  passing 
through  the  optic  nerve  and  the  lens  in  a  plane  parallel  to  the  hya- 
loid artery,  and  bisecting  the  hyaloid  canal.  The  lens  has  been 
slightly  displaced  in  the  act  of  sectioning,  causing  some  disarrange- 
ment of  the  adjacent  structures,  especially  of  the  fibers  of  the 
zonula  ciliaris.  The  vitreous  body,  however,  is  in  perfect  condition. 
The  section  was  stained  in  H  eld's  molybdic  haematoxylin,  which 
shows  very  clearly  the  delicate  fibers,  but  unfortunately  overstains 
the  remaining  structures.  The  small  crystals  found  scattered  here 
and  there  are  owing  to  mercuric  chloride  used  in  killing  and  fixing 
the  material. 

The  salient  feature  of  the  vitreous  body  at  this  period  of  de- 
velopment, compared  with  figure  5,  is  the  absence  of  the  large  meso- 
dermal ingredient  of  the  previous  stages  of  development.  All  that 
remains  of  the  extensive  hyaloid  arterial  system  is  the  main  trunk, 
the  hyaloid  artery,  extending  through  the  entire  posterior  chamber 
of  the  eye,  from  the  optic  nerve  to  the  lens,  to  which  it  still  ad- 
heres. Its  various  branches  have  already  disappeared.  A  closer 
examination  of  the  vitreous  body,  however,  reveals  a  large  number 
of  cells  in  various  stages  of  disintegration.  The  methods  used  in  the 
preparation  of  the  material  and  the  heavy  stain  make  it  impossible 


19 

to  determine  the  structure  and  the  nature  of  these  cells,  but  nowhere 
does  there  appear  any  connection  between  them  and  the  vitreous 
body  fibers. 

The  vitreous  body  proper  is  represented  by  a  great  mass  of  very 
delicate  fibers,  arising  exclusively  from  a  small  region  of  the  anterior 
portion  of  the  retina,  the  pars  coeca  retince.  From  here  they  descend 
in  fairly  heavy  bundles  towards  the  center  of  the  bulbus  in  the 
region  of  the  optic  nerve.  Several  of  these  fiber  bundles  pass  closely 
along  the  retina,  while  the  others  grow  slightly  inward  in  the  direc- 
tion of  the  lens  and  then  turning  backward  join  the  first  near  the 
optic  nerve  (Figure  18).  Between  these  two  heavier  portions  of 
the  vitreous  body  we  have  a  rather  large  space  filled  with  an  irregu- 
lar mass  of  fibrous  tissue.  The  vitreous  body,  therefore,-  is  com- 
posed of  two  rather  prominent  masses  or  layers  of  fibers,  the  one 
forming  the  outer  portions  near  the  retina,  and  the  other  lining  the 
hyaloid  canal,  while  the  intervening  region  contains  a  very  loosely 
arranged  fibrous  mass.  The  outer  portion  of  the  vitreous  fibers  has 
been  quite  generally  held  to  be  a  special  membrane  and  called  the 
hyaloid  membrane.  Careful  investigation  shows  that  the  vitreous 
fibers  are,  indeed,  more  closely  arranged  in  this  region,  but  they  do 
not  coalesce  to  form  a  distinct  membrane.  The  internal  limiting 
membrane  of  the  retina  seems  rather  to  be  common  to  both  the  retina 
and  the  vitreous  body.  This  view  is  held  by  most  recent  investiga- 
tors (Kolliker,  Szily,  Wolf  rum,  Mavas,  Magitot,  Seef  elder,  Szent- 
Gyorgyi),  who  insist  that  the  supposition  of  the  existence  of  a  mem- 
brane enveloping  the  vitreous  body  and  distinct  from  the  internal 
limiting  membrane  of  the  retina  is  not  based  upon  fact.  In  this 
connection  we  may  call  attention  to  the  peculiar  fact  that,  when 
shrinkage  of  the  vitreous  body  takes  place,  the  retinal  membrane 
quite  generally  adheres  to  the  vitreous  body,  which  shows  the  inti- 
mate union  of  the  two.  The  inner  mass  of  vitreous  body  fibers 
separates  the  vitreous  body  proper  from  the  so-called  hyaloid  canal. 
This  portion  of  the  vitreous  body,  the  existence,  size,  and  real  struc- 
ture of  which  have  been  the  subject  of  much  controversy,  is  clearly 
shown  in  figure  18. 

Figure  17  shows  its  relation  to  the  other  parts  of  the  eye,  its  rela- 
tive size  and  its  shape.  It  roughly  resembles  a  funnel,  with  its  mouth 
towards  the  lens,  and  the  stem  surrounding  the  optic  papilla.  While 
quite  narrow  in  the  inner  portion  of  the  eye,  it  widens  very  much 


20 

and  extends  not  to  the  lens,  but  to  the  ciliary  portion  of  the  retina, 
which  gives  rise  to  the  vitreous  fibers.  Its  vast  size,  compared  with 
the  diameter  of  the  hyaloid  artery,  seems  to  dispose  at  once  of  the 
theory  that  the  hyaloid  canal  simply  represents  the  portion  of  the 
vitreous  body  formerly  occupied  by  that  blood  vessel.  Its  walls  are 
formed  by  the  vitreous  fibers  which  in  many  sections  have  all  the 
appearances  of  a  real  membrane  (Figure  18).  This  impression- is 
heightened  by  closer  study.  Still  we  hesitate  to  describe  this  por- 
tion as  a  special  membrane.  We  rather  incline  to  the  belief  that  the 
membranous  appearance  is  owing  to  the  thickness  of  the  section, 
which  in  this  case  is  not  less  than  400  microns.  The  fibrous  nature 
of  this  structure  seems  to  be  quite  plainly  shown  in  the  upper  left- 
hand  portions  of  figure  18.  It  is  not  improbable,  however,  that  the 
fibers  are  held  together  by  the  thickened  fluids  of  the  vitreous*  body, 
giving  it  the  firm  membranous  appearance  it  possesses.  This  portion 
of  the  vitreous  body,  although  generally  called  the  hyaloid  canal,  is 
in  reality  not  a  canal.  It  is  not  an  open  tube  without  structural 
elements,  because  its  interior  is  filled  with  an  irregular  mass  of 
tissue,  not  unlike  that  of  the  central  portions  of  the  vitreous  body 
enclosed  between  the  outer  and  inner  fiber  bundles  already  described 
and  illustrated  in  figure  18. 

To  complete  the  description  of  the  eye  at  this  period  we  call 
attention  to  another  new  structure  which  has  appeared  in  the  mean 
time,  the  zonula  ciliaris  (Figure  15).  The  sketch  is  prepared  from 
a  section  of  the  left  eye  of  the  same  embryo  which  furnished  the 
material  for  the  illustrations  on  plate.  The  zonula  ciliaris  consists 
of  a  number  of  rather  strong  fibers  between  the  pars  ciliaris  retina? 
and  the  lens.  They  arise,  as  is  clearly  shown  in  many  sections,  from 
the  region  of  the  retina,  that  produces  the  vitreous  fibers,  only 
slightly  anterior  to  the  latter.  Retina,  vitreous  body,  and  zonula 
ciliaris,  therefore,  are  genetically  most  intimately  related. 

Keeping  in  mind  the  structure  of  the  eye  at  this  rather  advanced 
stage  of  embryonic  life,  we  may  now  attempt  to  trace  the  develop- 
ment of  the  various  parts  of  the  vitreous  body  up  to  this  time.  In 
embryos  of  80  mm  length,  the  hyaloid  vascular  system  consists  of 
the  main  trunk  and  a  number  of  branches,  some  of  which  surround 
the  posterior  half  of  the  lens,  while  the  rest  form  a  complex  system 
in  the  outer  portion  of  the  vitreous  body  near  the  retina.  The 
entire  system  is  only  a  temporary  formation,  whose  function  is  to 
furnish  nourishment  to  the  rapidly  developing  lens,  and  no  doubt, 


21 

also  to  the  vitreous  body  and  to  part  of  the  retina,  which  for  a  long- 
time has  no  blood  vessels  of  its  own.  This  functional  interde- 
pendence of  blood  vessels,  vitreous  fibers,  and  retina  might  offer  a 
teleological  explanation  for  the  intimate  protoplasmic  union  of  these 
parts  described  in  chapter  II.  As  soon  as  the  hyaloid  system  has 
discharged  this  nutritive  function,  a  process  of  resorption  sets  in. 
This  process  does  not  always  begin  from  the  extremities  of  the 
branches;  it  first  manifests  itself  by  a  general  decrease  in  the  dia- 
meter of  the  blood  vessels,  which  may  thus  be  cut  up  into  a  number 
of  parts  found  scattered  in  various  places  of  the  vitreous  body. 
These  parts  gradually  disintegrate  and  give  rise  to  many  cellular 
elements  which  are  met  with  in  more  advanced  stages  of  develop- 
ment and  sometimes  even  in  the  eyes  of  adult  animals.  They  are 
the  remnants  of  the  hyaloid  vascular  system.  The  gradual  resorp- 
tion of  the  blood  vessels  does  not  proceed  in  a  uniform  manner  in 
all  embryos,  as  a  comparison  of  embryos  of  130,  150,  and  180  mm 
length  shows,  but  in  the  eyes  of  embryos  of  200  mm,  only  the  main 
trunk,  the  hyaloid  artery  proper,  remains  (Figure  17).  It  may  be 
added  here  that  the  main  trunk  was  found  also  in  a  practically 
mature  fetus  12  inches  in  length,  which  makes  it  probable  that  com- 
plete resorption  of  the  hyaloid  artery  takes  place  at  the  time  of 
birth  or  even  later.  In  the  eye  of  a  full  grown  animal,  a  piece  of 
the  hyaloid  artery,  about  6  mm  long,  was  still  present  attached  to 
the  lens.  Together  with  the  hyaloid  system  the  remaining  meso- 
dermal  elements  also  undergo  a  process  of  disintegration. 

What  then  is  the  fate  of  the  fibrous  network  which  we  found  in 
such  intimate  union  with  the  mesoderm  in  the  previous  stages  of 
development  f  It  is  probable  that  a  portion  of  it  also  disintegrates 
and  is  resorbed.  But  it  is  no  less  probable  that  the  remaining  por- 
tions make  up  the  loose  fibrous  tissue  found  in  the  hyaloid  canal  and 
in  the  more  fluid  parts  of  the  vitreous  body.  The  reasons  for  this 
assumption  will  be  given  below. 

We  must  first  turn  our  attention  to  another  structure,  a  clear 
conception  of  the  formation  and  the  significance  of  which  will  throw 
more  light  on  the  present  investigation.  This  structure  is  the  hya- 
loid canal.  We  have  already  called  attention  to  the  wide  difference 
in  the  diameter  of  the  hyaloid  artery  and  the  so-called  hyaloid  canal, 
and  expressed  our  doubts  that  the  latter  represents  nothing  but  the 
cavity  left  for  a  time  after  the  former  has  been  resorbed.  This 


22 

explanation  is  defended  most  persistently  by  Wolfrum,  who  main- 
tains moreover  that  the  hyaloid  canal  is  not  found  in  the  eyes  of 
adult  animals,  except  in  connection  with  remnants  of  the  hyaloid 
artery.  The  discussion  of  the  latter  statement  we  reserve  until 
later.  For  the  embryonic  eye,  however,  we  can  not  accept 
Wolf  rum's  explanation. 

Equatorial  sections  prepared  for  the  purpose  of  ascertaining 
the  precise  time  of  the  first  appearance  of  the  hyaloid  canal  show 
that  it  is  formed  in  embryos  between  130  and  150  mm  length.  From 
the  first  it  shows  its  characteristic  funnel-like  shape,  its  size  consid- 
erably exceeding  the  diameter  of  the  blood  vessel  (Figure  20).  The 
latter  most  frequently  appears  in  the  center  of  the  canal  and  shows 
no  relation  to  its  walls  (Figure  18).  In  a  number  of  longitudinal 
sections  of  the  eyes  of  embryos  ranging  from  150  to  180  mm  length, 
the  slowly  degenerating  hyaloid  system  consists  of  the  main  trunk, 
the  hyaloid  artery,  and  several  branches  surrounding  it  in  a  manner 
not  unlike  the  supporting  framework  of  a  tent.  At  this  time  there 
is  observed  likewise  an  increased  growth  of  the  vitreous  fibers  from 
the  ciliary  region  of  the  retina.  A  portion  of  these  fibers,  as  was 
shown  above,  takes  its  course  toward  the  lens  and  then  turns  inward 
toward  the  centre  of  the  eye.  It  is  this  portion  which  is  so  prom- 
inent in  figure  18.  Now  it  seems  to  us  very  probable  that  this 
peculiar  direction  is  given  to  the  fibers  by  the  branches  of  the  blood 
vessels.  In  many  sections,  parts  of  the  latter  are  almost  invariably 
found  in  a  plane  parallel  to  the  vitreous  fiber  bundles  (Figure  21). 
But  whereas  the  blood  vessels  finally  disappear,  the  direction  given 
to  the  fibers  remains,  thus  determining  the  outline  and  shape  of  the 
hyaloid  canal  of  which  they  form  the  membrane-like  wall. 

This  denser  formation  of  the  vitreous  fibers,  descending  in  a  cir- 
cular band  from  the  ciliary  retina  encloses  a  large  portion  of  the 
original  vitreous  body  which  forms  the  fibrous  contents  of  the  hya- 
loid canal.  This  irregular  fibrous  mass  may,  therefore,  be  regarded 
as  the  remnant  of  the  central  portion  of  the  vitreous  body  of  the 
preceding  period  of  development.  A  similar  explanation  is  offered 
for  the  irregular  fibrous  tissue  between  the  two  heavier  layers  of 
vitreous  fibers  in  the  lateral  parts  of  the  eye.  Thus  the  hyaloid 
canal  is  not  a  canal  in  the  generally  accepted  meaning  of  the  word, 
yet  it  possesses  such  a  definite  structure,  and  it  is  so  sharply  marked 
off  from  the  rest  of  the  vitreous  body  that  it  deserves  a  special 


23 

name.  '  *  Hyaloid  portion  of  the'  vitreous  body ' '  might  be  more  de- 
scriptive of  its  real  structure.  Szent-Gyorgyi  suggests  tractus  hya- 
loideus  corporis  vitrei.  Its  essential  structure  is  given  at  this  stage 
of  development;  only  minor  modifications  are  observed  in  the  eye 
of  the  adult  animal. 

The  description  of  the  formation  of  the  hyaloid  canal  leads  us 
also  to  a  better  appreciation  of  the  structure  of  the  vitreous  body 
as  a  whole.  The  complex  structure  of  the  preceding  period,  owing 
to  the  invasion  by  great  masses  of  mesoderm,  has  disappeared 
through  a  process  of  disintegration  and  resorption,  and  has  given 
place  to  a  much  simpler  and  more  regular  arrangement  of  the  fibers. 
The  rather  strong  fibers  of  the  pars  ciliaris,  already  observed  in 
embryos  of  60  and  80  mm  length,  have  in  the  meantime  assumed 
the  appearance  of  fiber  bundles  (Figure  19),  the  arrangement  of 
which  has  already  been  described  at  length.  There  is  no  longer 
evidence  of  an  extensive  union  between  these  fibers,  each  bundle  be- 
ing more  or  less  independent  of  the  others.  But  their  place  of 
origin  is  the  same,  the  cells  of  that  portion  of  the  ciliary  retina, 
immediately  anterior  to  the  ora  serrata.  The  ectodermal  origin 
and  nature  of  the  permanent  vitreous  body  is,  therefore,  no  less 
certain  than  that  of  the  primitive  vitreous  body.  The  mesoderm 
has  no  share  in  its  production. 

The  vitreous  body  in  the  eye  of  the  adult  animal  differs  only 
in  minor  details  from  that  described  so  far.  Comparing  figures  17 
and  19,  we  notice  that  the  hyaloid  artery  has  entirely  disappeared. 
The  fibers  of  the  vitreous  body  and  the  zonula  ciliaris  have  essen- 
tially the  same  arrangement  and  structure  (Figures  15  and  16). 
The  shape  of  the  hyaloid  canal,  however,  has  slightly  changed.  By 
a  further  ingrowth  of  the  vitreous  fibers  in  the  region  of  the  lens, 
the  funnel-like  shape  of  the  preceding  stages  (Figures  17  and  18) 
has  given  place  to  a  structure  of  almost  uniform  diameter  through- 
out its  entire  length  (Figures  19  and  22).  This  tissue,  however, 
shows  no  tendency  to  condensation  or  growth  which  might  lead  to 
a  gradual  obliteration  of  the  canal.  The  latter  was  found  in  the 
eyes  of  every  specimen  examined,  forty  in  all.  Wolf  rum's  state- 
ment, therefore,  that  the  hyaloid  canal  is  not  a  constant  structure 
of  the  eye  of  the  adult  pig,  but  is  found  only  occasionally  and  then 
always  in  connection  with  remnants  of  the  hyaloid  artery,  is  not 
in  accordance  with  the  facts.  Only  in  two  eyes,  out  of  a  total  of 


24 

forty,  were  traces  of  the  hyaloid  artery  found,  and  even  in  these 
two  the  independent  formation  of  the  hyaloid  canal  was  plainly 
shown. 

Our  own  results  may  be  summed  up  thus :  the  hyaloid  canal,  or 
the  hyaloid  portion  of  the  vitreous  body,  formed  by  a  denser  ar- 
rangement of  the  vitreous  fibers  and  including  a  loose  and  irregular 
fibrous  tissue,  is  a  constant  structure  in  the  eye  of  the  adult  pig.  It 
is  of  almost  uniform  width  throughout,  and  extends  through  the 
entire  posterior  chamber  of  the  eye  from  the  optic  disc  to  the  lens, 
from  which  it  is  separated  by  the  thin  membranelike  lining  of  the 
fossa  patellaris.  In  rare  cases  it  contains  remnants  of  the  hyaloid 
artery,  which,  however,  show  no  relationship  to  its  walls.  The  hya- 
loid canal  in  the  eye  of  the  adult  pig,  is,  therefore,  not  a  temporary 
formation  nor  is  it  to  be  attributed  to  the  hyaloid  artery. 

Szent-Gyorgyi,  who  has  made  extensive  investigations  of  the 
structure  of  the  hyaloid  canal  in  the  eyes  of  adult  animals,  including 
the  pig,  maintains  that  the  relationship  of  the  vitreous  body  fibers 
to  the  ciliary  portion  of  the  retina  is  a  secondary  formation,  attrib- 
utable to  the  tendency  of  the  vitreous  fibers  to  attach  themselves  to 
any  structure  near  them,  and  that  in  consequence  this  relationship 
does  not  warrant  a  conclusion  as  to  the  origin  of  these  fibers,  which 
must  be  sought  rather  in  the  vitreous  body  itself  with  its  native 
faculty  of  growth  and  differentiation.  But  it  is  plain  that  the 
structure  of  the  adult  eye  does  not  of  itself  reveal  whether  the  con- 
ditions found  there  are  primary  or  secondary.  Nor  is  it  always 
safe  to  attempt  the  reconstruction  of  the  ontogeny  of  a  species  from 
its  supposed  phylogenetic  development.  Only  the  careful  study 
of  the  various  phases  of  embryonic  development  shows  whether  the 
union  between  the  vitreous  fibers  and  the  ciliary  retina  is  a  secon- 
dary formation  or  has  genetic  significance.  A  comparison  of  figures 
8  and  19  reveals  at  once  the  untenability  of  Szent-Gyorgyi 's 
opinion,  and  disposes  at  the  same  time  effectively  of  the  view  of 
Lenhossek,  adopted  and  modified  by  his  brilliant  followers,  v.  Szily 
and  Szent-Gyorgyi,  that  the  vitreous  body,  separating  from  its  place 
of  origin,  becomes  a  syncytium,  capable  of  independent  nutrition, 
growth,  differentiation  and  regeneration.  The  union  between  the 
vitreous  body  and  the  ciliary  retina  can  be  traced  uninterruptedly 
from  the  first  appearance  of  the  vitreous  fibers  to  the  formation  of 
the  permanent  vitreous  body.  The  latter,  therefore,  no  less  than 


25 


the  primitive,  and  the  essential  portions  of  the  secondary  vitreous 
body,  are  a  purely  ectodermal  derivative. 


CONCLUSIONS 

1.  The  vitreous  body  in  its  origin  is  a  purely  ectodermal  struc- 
ture and  consists  of  delicate  fibers,  the  protoplasmic  outgrowths  of 
the  basal  cells  of  the  retina. 

2.  With  the  development  of  ,the  hyaloid  vascular  system  and 
the   accession  of   other  mesodermal  elements,   an   intimate   union 
arises  between  the  vitreous  body  fibers  and  the  mesoderm,  so  that 
the  vitreous  body  at  that  stage  of  development  must  be  regarded  as 
a  tissue  of  derivatives  of  both  the  outer  and  the  middle  germ  layer. 

3.  The  union  between  the  vitreous  body  and  the  mesoderm  does 
not  destroy  the  dependence  of  the  vitreous  fibers  upon  the  retina, 
which  during  the  entire  embryonic  life  controls  the  development  of 
the  vitreous  body. 

4.  The  union  of  the  vitreous  body  and  the  mesoderm   is  not 
permanent.    It  is  dissolved  with  the  gradual  resorption  of  the  hya- 
loid vascular  system  and  the  disintegration  of  the  remaining  meso- 
dermal elements. 

5.  The  vitreous  body  in  its  final  development  is  again  a  purely 
ectodermal  structure,  consisting  of  great  masses  of  delicate  fibers, 
which  have  their  origin  in  the  basal  cells  of  the  ciliary  portion  of 
the  retina. 

6.  There  is  no  hyaloid  membrane  distinct  from  the  internal  lim- 
iting membrane  of  the  retina. 

7.  The  hyaloid  canal,  or  rather  the  hyaloid  portion  of  the  vitre- 
ous body,  is  found  in  all  advanced  stages  of  development  and  in  the 
eye  of  the  adult  animal. 

8.  The  hyaloid  canal  is  formed  by  a  thick,  membranelike  mass 
of  vitreous  fibers  and  contains  a  loosely  arranged  fibrous  tissue, 
which  may  be  regarded  as  the  remnant  of  the  secondary  vitreous 
body. 


LITERATURE 

List  of  authors,  to  whose  works  special  reference  is  made  in  this 
dissertation : 
Addario,  C.,  Sulla  struttura  del  vitreo  embrionale  e  dei  neonati; 

sulla  matrice  del  vitreo  e  suH'origine  della  zonula.    Pavia,  1902. 

tiber  die  Matrix  des  Glaskorpers  im  menschlichen  und 
tierischen  Auge.  Anat.  Anz.,  Bd.  XXI,  1902. 

Sulla  matrice  del  vitreo  nell'occhio  umano  et  degli  ani- 
mali.  Riforma  medic.,  an.  18,  1902. 

Sull  'apparente  membrane  limitante  della  retina  ciliare. 
Monit.  Zool.  Ital.,  an.  13,  1902. 

La  matrice  ciliare  delle  fibrille  del  vitreo,  loro  forma  et 
disposizione,  nonche  loro  rapporti  colla  neuroglia  della 
retina  visiva  perif erica  nell'occhio  umano  adulto.  Arch. 
Ottalm.,  vol.  XII,  1904. 

Arnold,  J.,  Die  Linse  und  das  Strahlenblattchen.    Graefe  u.  Saemich 
Handb.  d.  ges.  Augenheilk.,  Bd.  Ill,  Kap.  II,  1874. 

Bach,  L.,  und  Seefelder,  R.,  Atlas  zur  Entwicklungsgeschichte  des 
menschlichen  Auges.    Leipzig  und  Berlin,  1914. 

Bribach,  R.,  tiber  den  Zentralkanal  des  Glaskorpers.    Arch.  Opht., 
Bd.  LXXVI,  1910. 

Cirincione,  G.,  Sullo  stato  odierno  della  questione  riguardante  la 
genesi  del  vitreo.    Siena,  1905. 

tiber  die  Genese  des  Glaskorpers  bei  Wirbeltieren.  Cen- 
tralbl.  prakt.  Augenheilk.,  27  Jahrg.,  1903. 

Fischel,  A.,  tiber  die  Regeneration  der  Linse.     Anat.  Hefte,  Bd. 
XIV,  1900. 

Franz,  V.,  Histogenetische  Theorie  des  Glaskorpers.     Arch,  vergl. 
Opht.,  Ill  Jahrg.,  1912. 

Haemers,    A.,    Regeneration    du    corps   vitre.      Arch.    d'Opht.,    t. 
XXIII,  1903. 

Held,  H.,  tiber  die  Neuroglia  marginalis  der  menschlichen  Gross- 
hirnrinde.    Monatsschr.  f.  Psych,  u.  Neurol.,  Bd.  LX,  1905. 

Die  Entwicklung  des  Nervengewebes  bei  Wirbeltieren. 
Leipzig,  1909. 


27 

Kessler,  L.,  Untersuchungen  iiber  die  Entwicklung  des  Auges,  an- 
gestellt  am  Hiihnchen  und  Triton.  Inaug.  dissert.,  Dorpat, 
1871. 

Tiber  die  Entwicklung  des  Glaskorpers.  Dorpat  mediz. 
Zeitschr.,  1874. 

Zur  Entwicklung  des  Wirbeltierauges.    Leipzig,  1877. 

Kolliker,  A.  v.,  Entwicklungsgeschichte  des  Menschen  und  der 
hoheren  Wirbeltiere.  Leipzig,  1861. 

Die  Entwicklung  und  Bedeutung  des  Glaskorpers.  Zeit- 
schr. wiss.  ZooL,  Bd.  LXXVI,  1903. 

Lenhossek,  M.  v.,  Die  Entwicklung  des  Glaskorpers.    Leipzig,  1903 
Die  Entwicklung  und  Bedeutung  der  Zonulafasern  nach 

Untersuchungen  am  Hiihnchen.     Arch.   mikr.     Anat.,  Bd. 
LXXVII,  1911. 

Lillie,  Frank  E.,  The  Development  of  the  Chick.    New  York,  1908. 

Mavas,  J.,  Note  sur  1'origine  des  fibres  de  la  zonule  de  Zinn.  C.  B. 
Soc.  de  Biol.,  t.  LXIV,  1908. 

Recherches  sur  1 'anatomie  et  la  physiologic  de  la  region 
ciliaire  de  la  retine.  (Secretion  de  1'humeur  aqueuse.  Ori- 
gine  des  fibres  de  la  zonule  de  Zinn.)  These  de  doctorat  en 
medecine,  Lyon,  1910. 

Recherches  cytologiques  et  physiologiques  sur  la  retine 
ciliaire.  Arch,  d'anat.  micr.,  t.  XII,  1910. 

Mavas,  J.,  et  Magitot,  A.,  Etude  sur  le  developpment  du  corps  vitre 
et  de  la  Zonule  chez  I'Homme.  Arch,  d'anat.  micr.,  XIV,  1912. 

Les  cellules  du  corps  vitre  de  1'oeil  humain  (leur  origine, 
leur  signification,  et  leur  role  physiologique  dans  la  forma- 
tion des  liquides  intra-oculaire).  Ann.  d 'Oculist.,  1913. 

Parker,  J.  T.,  and  Haswell,  W.  A.,  A  Text-Book  of  Zoology.  Lon- 
don, 1910. 

Pee,  van,  Recherches  sur  1 'origine  du  corps  vitre.  Arch,  de  Biol., 
t.  XIX,  1902. 

Prentiss,  Ch.  W.,  and  Arey,  L.  B.,  A  Laboratory  Manual  and  Text- 
Book  of  Embryology.  Sec.  Edit.,  Philadelphia,  1917. 

Babl.  C.,  Uber  den  Bau  und  die  Entwicklung  der  Linse.  Leipzig, 
1900. 


28 

Ketzius,  G.,  Uber  den  Bau  des  Glaskorpers  und  der  Zonula  Zinnii  in 
dem  Auge  des  Menschen  und  einiger  Tiere.  Biol.  Untersuch., 
Neue  Folge,  VI,  Stockholm,  1894. 

Sauri,  R.,  Se  reproduce  el  humor  vitreo?  Cron.  med.-quir.  de  la 
Habana,  vol.  XL,  1914. 

Scholer,  H.,  De  oculi  evolutione  in  embryonibus  gallinaceis.  Inaug. 
Dissert.  Dorpati,  1848. 

Seefelder,  R.,  Beitrage  zur  Histogenese  und  Histologie  des  Netzhaut- 
Pigmentzirkels  und  des  Sehnerven.  Graefe  Arch.  Opht.,  Bd. 
LXXIII,  1910. 

Szent-Gyorgyi,  A.  v.,  Der  Canalis  hyaloideus  im  Auge  des  Schweines. 
Arch.  f.  Opht.,  Bd.  85,  1913. 

Untersuchungen  liber  den  Glaskorper  der  Amphibien  und 
Reptilien.  Arch.  mikr.  Anat,,  Bd.  LXXXV,  1914. 

Die  histologische  Darstellung  des  Glaskorpers.  Zeitschr. 
wiss.  Mikr.,  Bd.  XXXI,  1914. 

Szily,  A.  v.,  Zur  Glaskorperfrage.  Eine  vorlaufige  Mitteilung. 
Anat.  Anz.,  Bd.  XXIV,  1904. 

Zur  Glaskorperfrage.    Anat.  Anz.,  Bd.  XXIV,  1904. 

tiber  den  gegenwartign  Stand  der  Frage  hinsichtlich  der 
Genesis  des  Glaskorpers.  Arch.  f.  Augenheilk.,  Bd.  L,  1904. 

Histiogenetische  Untersuchungen.  I.  Die  Entstehung  von 
Knochen  aus  dem  Ektoderm.  Anat.  Hefte,  Bd.  XXXIII, 
1907. 

tiber  das  Entstehen  eines  fibrillaren  Stiitzgewebes  im 
Embryo  und  dessen  Verhaltnis  zur  Glaskorperfrage.  Anat. 
Hefte,  Abt.  1,  Bd.  XXXV,  1908. 

Tornatola,  S.,  Sull'origine  e  la  natura  del  vitreo.  Arch,  di  Ottalm., 
Vol.  V,  1897. 

Sull'origine  del  vitreo.  Ann.  di  Ottalm.  e  Lavori  delle 
clin.  ocul.  di  Napoli,  Vol.  XXXI,  1903. 

Sulla  membrane  limitante  interna  della  retina  nei  Verte- 
brati.  Anat.  Anz.,  Bd.  XXIV,  1904. 

Virchow,  R.,  Notiz  liber  den  Glaskorper.  Arch.  path.  Anat.  u. 
Phys.,  Bd.  IV,  1851. 

tiber  den  menschlichen  Glaskorper.    Ib.,  Bd.  V,  1853. 


29 

Virchow,  H.,  Facher,  Zapfen,  Leisten,  Polster,  Gefasse  in  Glaskor- 
perraum  von  Wirbeltieren,  sowie  damit  in  Verbindung  stehende 
Fragen.  Ergeb.  Anat.  u.  Entw.-Gesch.,  Bd.  X,  1900. 

Wolfrum,  M.,  Zur  Genese  des  Glaskorpers.  Ber.  33  Vers.  Opht. 
Gesellsch.,  Heidelberg,  1906. 

Zur  Entwickluiig  und  normalen  Struktur  des  Glaskor- 
pers. Arch.  Opht.,  Bd.  LXV,  1907. 

Zur  Frage  nach  der  Existenz  des  Glaskorperkanales.  Ib., 
Bd.  LXVII,  1908. 

1st  das  konstante  Vorkommen  des  Glaskorperkanales 
Kunstprodukt  oder  praformierte  Struktur?  Ib.,  Bd. 
LXXIII,  1909. 

Zur  Bemerkung  Professors  Stilling  betreffs:  Zur  Frage 
aach  der  Existenz  der  Glaskorperkanale.  Ib.,  Bd.  LXIX 
and  LXX,  1909. 


31 


EXPLANATION  OF  THE  FIGURES 


32 


PLATE  I. 


A.  W.  Fromm  photog. 


33 


PLATE   I. 

Figures  1,  2,  4  and  5  were  magnified  100  diameters,  figure  3 
was  magnified  150  diameters,  the  entire  plate  was  then  reduced 
to  two-thirds  in  reproduction. 

Fig.  1.  Longitudinal  section  of  eye  of  9  mm  embryo.  The  sec- 
tion is  slightly  posterior  to  the  optic  stalk,  a  part  of  which  is  shown 
between  pigment  layer  and  portion  of  the  diencephalon  visible  to 
right. 

Fig.  2.  Longitudinal  section  of  eye  of  20  mm.  embryo.  The 
section  shows  plainly  the  connection  between  the  vitreous  body  and 
the  extraocular  mesenchyme,  which  is  invading  the  optic  cup 
through  the  perilenticular  opening;  also  extensive  vascular  system 
and  considerable  differentiation  of  central  portion  of  retina. 

Fig.  3.  Longitudinal  section  of  eye  of  8  mm  embryo.  Lens 
vesicle  complete,  choroid  fissure  wide  open,  mesenchyme  pressing 
into  optic  cup  through  choroid  fissure. 

Fig.  4.  Horizontal  section  of  eye  of  12  mm  embryo.  Hyaloid 
artery  has  penetrated  to  lens  vesicle. 

Fig.  5.  Longitudinal  section  of  eye  of  25  mm  embryo.  Hya- 
loid artery  entering  through  optic  stalk,  has  given  rise  to  extensive 
vascular  system  which  penetrates  larger  part  of  vitreous  body. 


34 


PLATE  II. 


Fromm  &  Herring  del. 


35 


i 


PLATE  II. 

Figures  6-9  were  drawn  with  a  camera  lucida,  Bausch  and 
Lomb  microscope,  ocular  10,  objective  4.  Plate  reduced  to  two- 
thirds  in  reproduction. 

Fig.  6.  Longitudinal  section  of  eye  of  5  mm  embryo.  First 
stage  in  the  formation  of  the  optic  cup  and  the  lens  vesicle. 

Fig.  7.  Longitudinal  section  of  eye  of  3.5  mm  embryo,  showing 
primary  optic  vesicle.  Note  layer  of  mesenchyme  between  optic 
vesicle  and  body  ectoderm. 

Fig.  8.     Detail  of  section  of  eye  of  9  mm  embryo. 

Fig.  9.  Detail  of  longitudinal  section  of  eye  of  11  mm  embryo, 
showing  general  arrangement  of  vitreous  fibers. 


mK?2i<WK 


Frorart  &  Herring  del. 


PLATE  III. 

Figures  10-12  were  drawn  with  a  camera  lucida,  Bausch  and 
Lomb  microscope,  ocular  5,  objective  16.    Plate  reduced  to  one-half. 

Fig.  10.  Detail  of  section  of  eye  of  25  mm  embryo. 
Fig.  11.  Detail  of  section  of  eye  of  80  mm  embryo. 
Fig.  12.  Detail  of  section  of  eye  of  35  mm  embryo. 


38 


14 


PLATE  IV. 


A.  W.  Fromm  photog. 


39 


PLATE  IV. 

Fig.  13.  Cross-section  of  vitreous  body  of  23  mm  embryo, 
showing  the  many  fibrous  outgrowths  of  the  hyaloid  arterial  system 
and  of  the  numerous  free  mesoderm  cells,  also  the  union  of  these 
mesodermal  elements  with  the  vitreous  body.  Magnification  350 
diameters. 

Fig.  14.  Section  of  eye  of  100  mm  embryo.  Blood  vessels  form 
two  distinct  systems,  one  surrounding  the  lens,  and  the  other  lying 
close  to  the  retina.  Numerous  fibers  of  blood  vessels.  Note  espe- 
cially fibers  running  parallel  to  retina.  Magnification  95  diameters. 


40 


16 


PLATE  V. 


Fromm  &  Herring  del. 


41 


PLATE  V. 

Figures  15  and  16.  Zonula  ciliaris  of  eye  of  225  mm  embryo 
and  of  adult  animal.  Drawn  with  camera  lucida,  Bausch  and  Lomb 
microscope,  ocular  5,  objective  16.  Plate  reduced  to  two-thirds. 
Portion  of  lens  (below)  and  of  ciliary  retina. 


PLATE  VI. 


A.  W.  Fromm  photog. 


43 


PLATE  VI. 

Fig.  17.  Horizontal  section  of  eye  of  225  mm  fetus,  showing 
hyaloid  canal  with  hyaloid  artery,  and  origin  of  vitreous  fibers  from 
ciliary  retina.  Magnification  6  diameters. 

Fig.  18.     Central  portion  of  fig.  17  further  enlarged. 

Fig.  19.  Horizontal  section  of  eye  of  adult  pig,  showing  hya- 
loid canal,  vitreous  fibers,  and  zonula  ciliaris.  Magnification  2.5 
diameters. 

Fig.  20.  Cross-section  of  hyaloid  canal  of  250  mm  fetus,  with 
hyaloid  artery  in  lower  centre.  Magnification  20  diameters. 

Fig.  21.  Cross-section  of  hyaloid  canal  of  150  mm  embryo. 
Magnification  20  diameters. 

Fig.  22.  Cross-section  of  hyaloid  canal  of  eye  of  adult  pig. 
Magnified  20  diameters. 


VITA  AUCTORIS 

The  writer  of  this  dissertation  was  born  in  Volkerode,  in  the 
Province  of  Saxony,  Germany,  March  26,  1883.  After  attending 
the  public  school  of  his  native  town  for  seven  years,  he  came  to  this 
country  in  1895  and  entered  St.  Joseph  Seminary,  Teutopolis,  Illi- 
nois, from  which  he  was  graduated  in  June,  1902.  In  the  same 
month  he  entered  the  Order  of  Friars  Minor  in  the  Province  of  the 
Sacred  Heart,  pursuing  his  rhetorical  and  philosophical  studies  in 
Chicago,  Illinois,  from  1903  to  1906,  and  his  theological  studies  in 
St.  Louis,  Missouri,  from  1906  to  1910.  He  was  ordained  to  the 
holy  priesthood  on  June  25,  1909.  From  1910  to  1917  he  was  a 
member  of  the  faculty  of  St.  Joseph  Seminary,  Teutopolis,  Illinois. 
He  then  spent  two  years  at  the  University  of  Chicago  in  the  study 
of  biology,  physiology,  and  psychology,  and  three  semesters  at  the 
Catholic  University  of  America,  Washington,  D.  C. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 


Return  to  desk  from  which  borrowed. 
This  book  is-DUEton  the  last  (date  stamped  below. 


UEC 


*  1950 


MAY  14  1954 

APR  30 

JUL231959 


LD  21-100m-9,'48(B399sl6)476 


*  room,  A.I 

Vitrjsous, 
of  the  p: 


.       -      ^« 

body  . .  .in 

g 


BIOLOGY 
LIBRARY 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


